Intergeneric intragenic recombinants between trpA of E. coli and trpA of S. Typhimurium are being produced. Our objective is to obtain hybrid proteins consisting of different exchanged segments so that the function of such proteins may be assessed. We are comparing the promoter and operator region sequences of E. coli and S. typhimurium and are determining the base pair changes in operator constitutive mutants. We will attempt to clone the tryptophan synthetase structural genes from Neurospora crassa so that we may study its structure and regulation. An in vitro transcription system has been developed, with a cloned segment of the E. coli trp operon, with which we are studying rho mediated polarity termination in vitro. BIBLIOGRAPHIC REFERENCES: M. Manson & C. Yanofsky. Tryptophan operon regulation in interspecific hybrids of enteric bacteria. J. Bact. 126: 679-689 (1976). M. Manson & C. Yanofsky. Naturally occurring sites within the Shigella dysenteriae tryptophan operon severely limit tryptophan biosynthesis. J. Bact. 126: 668-679 (1976).